Offspring of mothers with gestational diabetes mellitus (GDM) are more likely to develop obesity, glucose intolerance, insulin resistance, and type 2 diabetes because of intrauterine exposure to maternal diabetes, although postnatal feeding may modify risk. A 'difficult' temperament coupled with postnatal feeding practices, such as lack of breastfeeding, early complementary and sugary foods may jointly predispose infants to rapid growth and later obesity which are key risk factors for future metabolic disease. We propose a secondary data analysis of a high-risk cohort of GDM mother-infant pairs (71% minority) enrolled in the Study of Women, Infant Feeding and Type 2 Diabetes after GDM Pregnancy (SWIFT;R01HD050625). From 2008-2011, SWIFT enrolled 1,035 GDM mothers who delivered a singleton, live birth e35 weeks at Kaiser Permanente hospitals. Temperament, dietary intake (e.g., breastfeeding, dietary intake, sugar-sweetened beverages), and anthropometry were assessed among 363 infants in the first year of life. Leveraging these existing data, the proposed research will elucidate, for the first time, relationships between infat temperament and health behaviors, and their impact on infant growth in GDM offspring. The study aims are: Aim 1: To characterize the relation of difficult temperament (i.e., poorer distress to limitations, and less soothability) to infant growth during the first year of life, Aim2: To evaluate potential mediators of the association between difficult temperament and rapid infant growth (i.e., less breast feeding, cereal added to the bottle, early introduction of juice/foods, and high intake of sugar-sweetened foods/beverages), and Exploratory Aim 3: To determine whether difficult infant temperament is associated with overweight at age 2-4 years. A difficult infant temperament may introduce a host of additional stressors to new mothers in addition to the stress of GDM pregnancy. Our proposed research addresses novel hypotheses about temperament and modifiable risk factors that may inform strategies for early life obesity prevention.